This invention relates to a method of making direct inking platen, and more particularly to improvements in the ink flow, wear resistance, and print definition characteristics thereof.
In the prior art, impact printers would either urge an inking surface toward the paper or vis a' vis. In U.S. Pat. No. 2,414,895 issued to M. Reynolds et al on Jan. 28, 1947, an operating bar impacts a porous print element through an ink filled flexible diaphragm-like reservoir. Compression of the reservoir and the mechanical engagement of the print element provided contact with the paper and also served to transfer ink from the reservoir to the print element.
Another form of impact printer termed a wire matrix printer is illustrated in U.S. Pat. No. 3,198,306 to R. A. Bachman on Aug. 3, 1965, and utilizes a plurality of individually operable dot printing elements such as spaced apart parallel wires. The wires are simultaneously projected in combination against an ink ribbon to effect printing of the whole character at once by the ribbon upon the paper. Characteristically, ribbon printing with wires suffers due to wearing of the wires impacting the ribbon and the deterioration of the ribbon due to the shredding of its fibers by the progressively worn and sharpened wires. While the exact mechanism of wearing of the wires is not fully understood, it is believed that it is due to a combination of factors such as chemical and hydraulic etching of the wire ends by the inking medium as well as mechanical impact deformation.
Of course, one approach is to eliminate the ribbon inking medium entirely. This may be accomplished by using self-inking paper. That is, the paper changes color due to localized pressure changes when impacted by the wires. This approach suffers the disadvantage of the high cost of specially treated paper, fragility, and tendency to discolor when mechanically handled.
Admittedly, the prior art is replete with many self-inking sponge-like structures ranging from the rubber used by Reynolds et al to the porous polyamide articles described in U.S. Pat. No. 3,022,542, issued to W. J. Davis on Feb. 27, 1962. Reference should also be made to the porous plastic printing structures shown in U.S. Pat. No. 3,303,146 to P. Chabiniak issued Feb. 7, 1967. The prior art teaches in general terms that an inking platen having microporous structure can be formed from the compression molding of particulate nylon or polyvinylchloride. These sponge-like structures, however, would be proverbially torn to shreds under repeated wire firings in a wire matrix printer, for example. It is also the case that the impacting of sponge-like structures, even with the same force, results in dissimilar quantities of liquid being ejected therefrom. Lastly, such structures frequently have their pores randomly distributed. This means that the print character may lack good definition i.e., the dot print elements lack regular and uniform spacing.